Asked if he knew where the suspects went, he said Suspect No. 2 had gone west on Boylston Street after planting the bomb. It wasn’t known where the other suspect went, he said.

He said, “As you can see, the quality of the photographs is quite good, but we will continue to work on developing additional images.” The officials said the images would be distributed to the media and posted on the FBI’s website. Video of the two men was also posted to Youtube.

The FBI asked people with photos, videos, and other information to e-mail them to boston@ic.fbi.gov. It also said people can call 1-800-CALL-FBI, prompt #3, to leave tips.

DesLauriers said investigators were particularly interested in interviewing witnesses who were in front of the Forum restaurant, site of one of the blasts.

The new details on the investigation came hours after President Obama visited Boston today, delivering an uplifting speech at the Cathedral of the Holy Cross and then visiting victims, their families, and hospital staff at Massachusetts General Hospital. Michelle Obama was expected to make similar visits. The president also met with hundreds of race volunteers at Cathedral High School, telling them “how proud the whole country is of you” for displaying “the best of the American spirit” in reacting to the blasts.

In Washington earlier today, Homeland Security Secretary Janet Napolitano testified today before a congressional committee that some of the video collected from near the Boston Marathon finish line had raised questions.

She said there were “individuals” the FBI would like to speak to. “I wouldn’t characterize them as ‘suspects’ under the technical term. But we need the public’s help in locating these individuals,” she said.

“The investigation is proceeding apace. This is not an NCIS episode. Sometimes you have to take time to properly put the chain together to identify the perpetrators, but everybody’s committed to seeing that that gets done in the right way,” she told Representative Michael McCaul, a Texas Republican, chairman of the Homeland Security Committee.

Asked by McCaul if officials considered it a foreign or domestic terror plot, she said, “Right now, we can’t say one way or the other.”

Also today, an executive with the company whose battery was possibly used as a power source for at least one of the bombs said that he had reached out to Boston police and the FBI, but had not heard back.

Benjamin Mull, vice president of business development and technology with the California-based company Tenergy, said he was aghast to see pictures distributed by national news outlets of possible remnants of one of the bombs, with a Tenergy Sub-C battery attached.

The batteries are made for specialty remote-controlled cars, and they are only known among more dedicated hobbyists and enthusiasts. The company said it has produced “tens of thousands” of the batteries over the past several years.

“It’s twisted because it’s a battery we built for a toy. To have it used this way is appalling,” Mull said. “Not in a million years would I have imagined. I don’t know anything about bombs, I don’t know how this would be used or could be used.”

Mull said his company does not sell them to large retailers, like Target or Walmart. Instead, he said, his company generally markets batteries to hobbyist stores or specialty battery stores.

“We’ve contacted Boston police and the FBI and will assist in any way we can,’’ Mull said. “We have not heard back from the FBI yet.”

The Marathon Monday explo­sions killed three people and injured more than 170, many of whom were grievously maimed. On Wednesday, author­ities confirmed the identity of the third victim, Boston University graduate student Lingzi Lu, who was from China. Martin Richard, an 8-year-old from Dorchester, and 29-year-old Krystle Campbell, a native of Medford, were also killed.

Fifty-seven people hurt in the blasts remained at Boston hospitals Thursday evening; six were in critical condition.

Obama signed an emergency declaration Wednesday for Massachusetts and ordered federal aid to supplement the local response to the bombings.

During an interfaith service at the cathedral, Obama received a standing ovation and sustained applause when he said: “When the Sox, the Celtics, the Patriots, the Bruins are champions again – to the chagrin of New York and Chicago fans – the crowds will gather and watch a parade go down Boylston Street. And this time next year, on the third Monday in April, the world will return to this great American city to run harder than ever and to cheer even louder for the one hundred and eighteenth Boston marathon. Bet on it!’’

The family of Medford’s Campbell issued a statement, saying they were devastated by the loss. “She was an incredible and loving sister, daughter, niece, granddaughter and friend. Her presence will be missed more deeply than words can express,” the statement said.

The family thanked first responders, medical professionals and others who aided Campbell and others hurt in the attack. It also thanked the public for their outpouring of support.

On Wednesday, the disclosure that a bomber was believed to have been seen on the Lord and Taylor surveillance video led to widespread media reports that a suspect was in custody, was under arrest, and was heading to US District Court in South Boston for an initial appearance.

Journalists and spectators converged on the Moakley ­courthouse, expecting a suspect to be brought in. But top law enforcement officials denied they had anyone in custody, and the courthouse was evacuated after a bomb threat. After a search of the building, employees and visitors were allowed back inside.

A 10-block area of the Back Bay remained closed to the public on Thursday as the investigation continued, city officials said. The area included Boylston Street, where the bombings occurred, and all side streets between Newbury Street and Huntington Avenue, though those thoroughfares were open, according to John Guilfoil, a spokesman for Mayor Thomas M. Menino. The area extended east to Clarendon Street, and was bounded on the west by Hereford, Dalton, and Belvidere streets.

The pieces of evidence ­recovered so far include bomb fragments, from which experts have determined that at least one bomb was fashioned from a pressure cooker stuffed with explosives laced with nails and ball-bearings.

The maker of the pressure cooker, Fagor America Inc., ­issued a statement Wednesday saying the company has been contacted by investigators and is cooperating. “Our pressure cookers . . . are not intended to be used for any other purpose other than cooking,’’ the company said.

Shelley Murphy, John R. Ellement, and Mark Arsenault, as well as Globe correspondents Jeremy C. Fox and Lauren J. Dezenski, contributed to this report. Milton J. Valencia can be reached at mvalencia@globe.com. Follow him on Twitter @miltonvalencia.

BostonGlobe.com complimentary digital access has been provided to you, without a subscription, for free starting today and ending in 14 days. After the free trial period, your free BostonGlobe.com digital access will stop immediately unless you sign up for BostonGlobe.com digital subscription. Current print and digital subscribers are not eligible for the free trial.

Thanks & Welcome to Globe.com

You now have unlimited access for the next two weeks.

BostonGlobe.com complimentary digital access has been provided to you, without a subscription, for free starting today and ending in 14 days. After the free trial period, your free BostonGlobe.com digital access will stop immediately unless you sign up for BostonGlobe.com digital subscription. Current print and digital subscribers are not eligible for the free trial.